I haven't opened mine yet (preparing for Thanksgiving visitors and such), but I'm hoping that with 12 you play only 2 rounds. It's always bothered me that you pass to the left twice and to the right only once, anyway.

Well, I never realized it, but even the base game is no longer a three-round affair.

My first edition (blue box) said to play three rounds (at least I think it did and we always played it that way). The second (white box) and 12-player editions completely ignore the number of rounds. It just says that if you want to play again (that's more than one single round), then shake it up by changing directions or moving seats around or whatnot, but no specific mention that a "full game" is a series of a certain number of rounds.

So, I guess that the idea is to play it until you don't want to play anymore.